Gaseous depinking method



Jan. 23, 1951 D. G. sLovlN GASEOUS DE-PINKING METHOD Filed May 21, 1949BY U34 Y E. N R 0 T T A Patented Jan. `23, 1951 UNITED STATES PATENTOFFICE GASEUS DEPINKING METHOD Application May 21, 1949, Serial No.94,709

8 Claims.

This invention relates to a method for removing from vulcanized rubberarticles, particularly articles made of or containing elastic yarnshaving a core of vulcanized rubber and a wound covering of textile yarn,the pink discoloration which results from the presence of symmetricaldi-beta-naphthyl-para-phenylene diamine as an anti-oxidant in thevulcanized rubber. Still more particularly the invention relates to amethod of removing such pink discoloration from oven textile materialscomprising such elastic yarn, particularly when such woven textilematerial is in the form of cut pieces intended to be formed into agarment or the like, without wetting such materials with a liquid.

symmetrical di-beta-naphthyl-para-phenylene diamine is one of the bestall-around antioxidants for vulcanized rubber thus far developed.However, it exhibits the objectionable characteristic that it turns pinkwhen it is subjected to certain conditions, particularly when subjectedto light and oxidizing conditions. Under ordinary storage conditionspinking does not occur. However pinking appears to be catalyzed bylight, and certain oxidizing media such as nitric oxide fumes and ozone;and where these conditions prevail, pinking often becomes very rapid.Pinking readily occurs also during bleaching operations, `such as withchlorine and hydrogen peroxide, especially the former. This pinkdiscoloration changes the color or shade desired for the article and ishighly objectionable.

The problem of pinking as a result of the use of this anti-oxidant inrubber compositions and articles containing the same is especiallyserious in the case of light-colored vulcanized rubber compounds, suchas those having a light pastel color. or those which are white in color.The reason is that the development of the pink by decomposition or otherchange of the anti-oxidant changes the shade from that which is desired.

The problem of pinking is especially serious in the case of articles ormaterials made from or containing elastic yarn comprising a core ofvulcanized rubber containing the above antioxidant and a wound coveringof textile yarn. This problem is particularly serious where white orlight-colored textile yarns are used as the covering for the elasticcore or in association with the elastic yarn to make the fabric of whichthe article or material is formed or woven. The pinkdiscoloration whichoccurs as a result of the above anti-oxidant in the vulcanized rubbercore of the elastic yarn usually shows through the associated white orlight-colored textile yarns and bers, often in an irregular ornonuniform manner, and this is highly objectionable.

Elastic yarn of the type just referred to is described in detail in theAdamson Patent 1,822,847. This elastic yarn typically has a core ofelastic vulcanized rubber under tension with a covering of a pluralityof helical, preferably both right and left, windings which hold the coreelongated, the yarn having a predetermined capacity to stretch.

The elastic vulcanized rubber core of the elastic yarn may be made inany suitable manner. The method of making this core is well-known to theart and constitutes no part of the present invention. It is preferred toutilize rubber of a grainless character such as that obtained bycoagulation, drying and Vulcanization of suitably compounded rubberlatex especially the latex from Hevea brasz'lz'cnsis. It is preferred touse rubber thread of circular cross-section as the core. The latex maybe compounded, prior to coagulation, with suitable types and amounts ofrubber compounding ingredients such as sulfur or other vulcanizingagents, vulcanization accelerators, activators such as zinc oxide, andan effective amount of symmetrical di-beta-naphthyl-para-phenylenediamine as an anti-oxidant. The amount of the latter may Vary widely butshould be sufcient to be effective to prevent or greatly retard theoxidation of the rubber. The amount will usually range from 0.25 to 2.0%by weight based on the rubber present. The statements just made withreference to the compounding of the rubber core of elastic yarn applyequally to the compounding of rubber in any other form to which thepresent invention is applied.

The present invention is based on the discovery that the pinkdiscoloration which develops in vulcanized rubber-containing articles,such as woven textile fabrics comprising the above-described elasticyarn, as a result of the presence of symmetricaldi-beta-naphthyl-para-phenylene diamine in the rubber, can be completelyremoved therefrom by subjecting the pinked materials to the action ofgaseous sulfur dioxide. do not at this time know what reactions theanti-oxidant in question undergoes in pinking or in de-pinking inaccordance with my invention. It may be that the suliur dioxide gascombines with the traces of moisture always normally present inthe'goods being treated to form sulfurous acid, a weak acid with a mildreducing action, which effects the de-pinking. Alternatively, the sulfurdioxide may combine with the 3 anti-oxidant or its decompositionproducts in some manner to destroy the pink discoloration.

It appears that the action of the gaseous sulfur dioxide is not one ofbleaching, since the action of such bleaching agents as chlorine andhydrogen peroxide is to cause pinking rather than to remove it.

Whatever the explanation be, the exposure of the pinked material togaseous sulfur dioxide effects removal of the pink discoloration and thematerial which has been de-pinked in this manner is more resistant tosubsequent pinking than was the original material before the firstpinking, such as the normal woven fabric containing the elastic yarnhaving a core of vulcanized rubber containing the anti-oxidant inquestion. However, should the de-pinked material subsequently developpinking, such subsequent pinking can be easily removed by means of thepresent invention.

In practicing my invention, the pink'ed material is subjected to theaction of gaseous sufur dioxide in any suitable way, preferably byplacing the material in an atmosphere of sulfur dioxide gas. |I'hetreatment is edected while the material is maintained in its normallydry condition, i. e., without wetting the material which might causeshrinkage, distortion or other difficulties. Typically, the procedureofthe present invention is carried out by suspending the pinked materialon racks, pins, etc., in a closed container containing gaseous sulfurdioxide, either in concentrated form or diluted with a suit-ablediluent, usually air. A

The sulfur dioxide gas may be obtained from any suitable source. A veryconvenient way of forming the sulfur dioxide atmosphere is to place onthe bottom of the closed container a pan holding a water solution ofsodium hydrosulte. The solution may be of any convenient concentration,typically 10%. The solution is unstable and releases sulfur dioxidefumes. The whole may be allowed to stand at room temperature until thepinking has disappeared which may be a matter oi a few minutes or a fewhours, depending upon the severity of the pinking and the ease ofpenetration of the sulfur dioxide gas through the material. For exampleif the pieces of material are stacked, considerable time has to beallowed for penetration. Over-treatment with sulfur dioxide does no harmwhatsoever. An overnight treatment is often convenient. With regard tothe amount of sodium hydrosulte required, an amount equal to about 5% byWeight based on the weight of the goods is generally sufiicient but moreor less can be used as needed. The use of warm water in making up thesodium hydrosulte solution speeds up the evolution of sulfur dioxide gasand will generally shorten the time of treatment required.

, Alternatively, instead of placing an aqueous solution of sodiumhydrosuliite in the bottom of the container used for the treatment,sulfur dioxide from any other source, as ior example from a cylinder orgenerated from any simple chemical reaction, such as by the action ofconcentrated sulfuric acid upon sodium bisulite solution, may be used.Where sulfur dioxide gas from a cylinder is employed, the procedure maybe the same as that just described except that instead of using a pan ofthe sodium hydrosulte solution, arrangements are made for feeding thegas slowly to the container used for carrying out the treatment; anoutlet from the treatment container to the outside atmosphere ispreferablev to 4 prevent building up of dangerous pressures in thetreatment vessel.

It is dicult to specify exactly the amount of sulfur dioxide actuallyemployed in the treatment. However the use or amounts of the order offrom l to 2% by weight based on the weight of the fabric or othermaterial being treated is generally ample.

When the de-pinking action is complete, I prefer to subject thede-pinked material or goods to the action of gaseous ammonia (NH3) untilany acidic material present therein has been neutralized. This may bedone in the same container as that inv which the de-pinking wasaccomplished by removing the source of the sulfur dioxide andsubstituting a source of ammonia, for example a pan of aqua ammonia. Itwill be understood that the treatment With sulfur dioxide will usuallyleave some excess sulfur dioxide, which is mildly acidic, on and in thede-pinked material and that the ammonia will neutralize this acidity.Ammonia from any source may be used for this purpose. For example, I mayemploy ammonia from a cylinder, feeding the gaseous ammonia into theneutralizing chamber in a manner similar to that suggested above forsuliur dioxide. The treatment with ammonia gas should be of suiiicient'duration to completely neutralize any acidic material present in thedepinked goods. A relatively short exposure of from 5 to l() minuteswill often s'uice'. Again the length of the treatment will depend uponthe rapidity of penetration of the gas into the goods.

The treatment with ammonia may 'take place the same chamber as that inwhich the depinking was effected or in another chamber.

While my invention is often practiced in a batchwise manner, it will beunderstood by those skilled in the art that, if desired, it may becarried out continuously, for example by continuously passing the goodsor material to be de-pinked through an atmosphere of gaseous sulfurdioxide and thereafter continuously passing them through an atmosphereof gaseous ammonia.

It will be apparent fromV the foregoing that the material, whileundergoing treatment in accordance with my invention, is in its normallydry condition, i. e., any water content is so small that it is notvisible to the eye or detectable to the touch as water. Usually thewater content of the goods treated varies betweenl 1 and 7% by weightdepending on the type of material and the humidity prevailing.

Ivy invention is particularly advantageous in those cases where thegoods or other material turn pink after finishing and where nowetfinisning is normally required, since the expense of 're-wetting thegoods and re-drying them is elimihated by the present invention.Furthermore, most users ci the goods are not equipped'to remove the pinkby a wet bath treatment and would have to have it done by outside'n'ishers. In addition there are many cases where it is not permissibleto wet the goods because of the danger of shrinkage or distortion,danger of discoloraie'i, lViy new method takes care of such situationsand permits anyone to carry out the de-pinking process. The invention isespecially applicable Where the goods, such as fabrics containing theelastic yarn mentioned above, turn pink aftervthey have been cut intopatterns preparatory to sewing into a garment or other article; in suchcases a wet treatment generally' is out of the question since the cutsections display an objectionable tendency to shrink or become 5.distorted in shape. The gaseous treatment of my invention', involving nowetting whatever of the goods, is ideally adapted to de-pinking of suchout pieces.

The present invention has many other advantages which will be apparentto those skilled in the art. It provides a simple and effective way ofremoving the pink discoloration developed in rubber goods containing theabove anti-oxidant. It can be carried out with simple inexpensiveequipment. lt obviates use of complicated liquid treatment and dryingequipment. "iihe materials being treated need not be wet which asindicated above would often distort the goods and moreover would rduiresubsequent drying. While the pr o cedure of my invention is generallyused on elastic yarns and fabrics containing the same, it may be appliedto any rubber-'containing material which shows a pink discoloration dueto the presence of the anti-oxidant mentioned above.

In the accompanying drawing, which is substantially self-explanatory inthe light of the foregoing description, Fig. 1 shows a tank-like chamberi having a door 2 and within which there is an atmosphere of gaseoussulfur dioxide,

generated in any suitable manner. The cut pieces of goods 3 aresuspended on any suitable supporting' means such as a bar 4, in thisatmosphere. The sulfur dioxide atmosphere may be achieved by supplyingsulfurl dioxide gas from any suitable source through inlet 5. An outlet5 be provided as a bleed to prevent excessive pressure build-up ofsulfur dioxide in chamber l. in Fig. 2 the same pieces of goods 3 areshown as being subsequently treatedin a gaseous atmosphere of ammonia.The construction of the Fig. 2 chamber may be the same as that shown inFig. 1.

Having thus described my invention, what I claim and desire to protectby Letters Patent is:

1. A method of removing visible pink discoloration which has developedin a vulcanized rubber article as a resuit of the presence therein ofsymmetrical di-beta-naphthyl-para-phenylene diamine as an anti-oxidanttherefor which cornprises subjecting said article, while maintaining itin the dry condition, to the action of gaseous sulfur dioxide until thepink discoloration has disappeared.

2. A method of removing visible pink discoloration which has developedin a vulcanized rubber article as a result of the presence therein ofsymmetrical di-beta-naphthyl-para-phenylene diamine as an anti-oxidanttherefor which comprises subjecting said article, while maintaining itin the dry condition, to the action of gaseous sulfur dioxide until thepink discoloration has disappeared, and then subjecting the resultingarticle, while maintaining it in the dry condition, to the action ofgaseous ammonia until any acidic material present in said article hasbeen neutralized.

3. A method of removing visible pink discoloration which has developedin an article comprising elastic yarn having a core of vulcanized rubbercontaining symmetrical di-beta-naphthylpara-phenylene diamine as ananti-oxidant and a wound covering of textiie yarn, said discolorationresulting from the presence of said antioxidant, which comprisessubjecting said article, while maintaining it in the dry condition, tothe action of gaseous sulfur dioxide until the pink discoloration hasdisappeared.

4. A method of removing visibile pink discoloration which has developedin an article compris'- ing elastic yarn having a core of vulcanizedrubber containing symmetrical di-beta-naphthylpara-phenylene diamine asan an anti-oxidant and a wound covering of textile yarn, saiddiscoloration resulting from the presence of said anti-oxidant, whichcomprises subjecting said article, while maintaining it in the drycondition, to the action of gaseous sulfur dioxide until the pinkdiscoloration has disappeared, and then subjecting the resultingarticle, while maintaining it in the dry condition, to the action ofgaseous ammonia until any acidic material present in said article hasbeen neutralized.

5. A method of removing visibile pink discoloration which has developedin woven textile fabric comprising elastic yarn having a core ofvulcanized rubber containing symmetrical di-betanaphthyl-para-phenylenediamine as an antioxidant and a wound covering of textile yarn, saiddiscoloration resulting from the presence of said anti-oxidant, whichcomprises subjecting said fabric, while maintaining it in the dry condition, to the action of gaseous sulfur dioxide until the pinkdiscoloration has disappeared.

6. A method of removing visible pink discolor ation which has developedin woven textile fabric comprising elastic yarn having a core ofvulcanized .rubber containing symmetrical di-betanaphthyl-para-phenylenediamine as an antioxidant and a wound covering of textile yarn, saiddiscoloration resulting from the presence of said anti-oxidant, whichcomprises subjecting said fabric, while maintaining it in the drycondition, to the action of gaseous sulfur dioxide until the pinkdiscoloration has disappeared, and

vthen subjecting the resulting fabric, while maintaining it in the drycondition, to the action of gaseous ammonia until any acidic materialpresent in said fabric has been neutralized.

7. A method of removing visible pink discoloration which has developedin cut pieces of woven textile fabric comprising elastic yarn having acore of vulcanized rubber containing symmetricaldi-beta-naphthyl-para-phenylene diamine as an anti-oxidant and a woundcovering of textile yarn, said discoloration resulting from the presenceof said anti-oxidant, which pieces cannot be given a liquid treatmentwithout objectionable change in shape, which comprises subjecting saidcut pieces, while maintaining them in the dry condition, to the actionof gaseous sulfur dioxide until the pink discoloration has disappeared.

8. A method of removing visible pink discoloration which has developedin cut pieces of woven textile fabric comprising elastic yarn having acore of vulcanized rubber containing symmetricaldi-beta-naphthyl-para-phenylene diamine as an anti-oxidant and a woundcovering of textile yarn, said discoloration resulting from the presenceof said anti-oxidant, which pieces cannot be given a liquid treatmentwithout objectionable change in shape, which comprises subjecting saidcut pieces, while maintaining them in the dry condition, to the actionof gaseous sulfur dioxide until the pink discoloration has disappeared,then subjecting the resulting pieces, while maintaining them in the drycondition, to the action of gaseous ammonia until any acidic materialpresent therein has been neutralized.

DAVID G. SLOVIN.

(References on following page) REFERENCES CITED The followingreferencesA are off' record in theA le of this patent:

UNITED STATES PATENTS Number Name Date Sirtaine Oct. 16, 187.7 LappenMar. 16, 192.6 Schoner Apr. 9, 1929 Welffenstein Aug. 27, 1929.- 10Rosenberg Feb. 26, 1935 OTHER REFERENCES Austin, Fur Dressing and. FurDyeing," D. Van Nostrand Co., New York, 1922', pages 144,-170; pages147, 148, 153, 156, 157, 15.8 considered especially pertinent.

J owett, Stripping of Dyed Woolens and Other Textile Materials, J of theSociety of Dyers and Colourists, Aug. 1944, pages 197-200. Page 198considered especially pertinent.

Cox; Hair Dyes II, They Analyst, July 1940, pages. 393-398. Page 396considered especially pertinent.

3. A METHOD OF REMOVING VISIBLE PINK DISCOLORATION WHICH HAS DEVELOPEDIN AN ARTICLE COMPRISING ELASTIC YARN HAVING A CORE OF VULCANIZEDRUBPARA-PHENYLENE DIAMINE AD AN ANTI-OXIDANT AND A WOUND COVERING OFTEXTILE YARN, SAID DISCOLORATION RESULTING FROM THE PRESENCE OF SAIDANTIOXIDANT, WHICH COMPRISES SUBJECTING SAID ARTICEL, WHILE MAINTANNINGIT IN THE DRY CONDITION TO THE ACTION OF GASEOUS SULFUR DIOXIDE UNTILTHE PINK DISCOLORATION HAS DISAPPEARED.